I have a 2003 Nissan 350z with 110k miles on the odometer.

Every once in awhile, the motor will overheat. I have replaced the radiator, upper and lower coolant hoses, and the thermostat with brand new oem.

The radiator fans are working too.

The car will be fine for weeks and then suddenly, randomly, it will overheat. I'll pop the hood and the first thing I notice is there is 30-40 droplets of coolant that have shot out of the radiator cap, not very much at all, but its concerning because the radiator and the cap are brand new.

Before I replaced the radiator and cap, it would do the exact same thing with the old radiator and cap. That is why I replaced them.

I'm not sure why the cap is still spewing 30-40 droplets every once in awhile.

The coolant overflow tank always drains itself to the "min" mark after I fill it. The radiator itself will always be low after the overheat as well, it will be about 1-2 L of coolant low after it does its random overheat.

The headgasket is good I think, there is no coolant in the oil and no oil in the coolant.

I also have used a fill funnel to make sure no bubbles in the coolant. I've even had Firestone use a special tool that fills the coolant system via pressure to make sure there are no bubbles in the system.

After Firestone used this tool, the motor didnt overheat with regular use for over a month.

but today it overheated again. I refilled the radiator and it overheated again within 30 minutes after cooling off on the side of the road.

I've spoken to multiple mechanics and nobody seems to be able to figure out what's wrong.

Is there maybe a cracked hose? Or an air bubble? What am I missing? Has anybody dealt with this issue?

i hope someone has the answer for me because I am truly stumped on why this car randomly overheats with weeks-1 month and hundreds of miles between incidents.

I fill the radiator with a spill free funnel with the heat full blast on the climate control, while also using the bleeder valve by the firewall.

Thanks

-Gary

 

If it's not an air bubble it's a head gasket, you won't always have contamination BTW.

 

I had Firestone do a chemical block test and they said the headgasket was fine, do you still think its headgasket? I suppose its possible.

 

How long ago did you replace the radiator and radiator cap? I'd consider replacing the cap on the off chance it's defective after bleeding it once again.

 

I replaced the radiator cap like 90 days ago, brand new 0.9 bar

 

There are some cooling systems that require a tool called an "air lift" to remove all the air. I bought one back in the day to use on Neons. You might check into that approach, sounds like an air issue to me.

 

So I brought this car to a shop to have a compression test done. The car passed the compression test. along with a cooling system pressure test. So they said the headgasket is not leaking. and the radiator/cooling system is not leaking.

So i am wondering why the coolant level is dropping so rapidly. The coolant can only be going two places. Into the cylinder or on the floor. The shop said it passed a compression test and a cooling system pressure test.

So if the cylinder is fully pressurized and the radiator/cooling system is pressurized, where is 1.5L of coolant/2-3 weeks going?

These tests can't be right, I'm having another shop do a wet leakdown test this time to see if this shop i just got back from is lying... I think they might have not done the compression test and just said they did.

This shop i just got back from said its probably my thermostat.... but it is not my thermostat.

Any predictions? Thoughts? Thanks for reading.

 

The "compression" test as you call it is only a test that detects combustion gasses in the coolant system. If it comes up negative, coolant could still be leaking into the cylinders on a hot soak after shutdown, but I think not. I think you are still dealing with an air in the system problem. Over the years I have experienced brain racking coolant system issues and the majority of them wound up being air.

 

thanks for your reply. I do think it could be air in the system... but I am stumped where the coolant going? The radiator keeps dropping like 1.5L of fluid every once in awhile. Thats a lot of fluid. Where is it going? or what is happening to make it appear this way?

Also i had a shop that said they used a special tool that removes all the air bubbles... shouldn't i of been OK after that visit?

 

That would be the airlift I was referring to. Properly used, it will eliminate 100% of the air in the entire cooling system.

 

So i just confirmed that firestone did not use an airlift tool they used a system where they hook a vacuum up to one of the radiator hoses and sucks the coolant through as they force coolant into the radiator. I want to use an airlift tool now.

 

What you are describing is a coolant flush machine, not an airlift. BIG difference. Like I was saying before, there are several vehicles that have been on the market for years that you CANNOT remove air from the cooling system without an airlift. Get in your car, drive it a few miles to warm it up and then turn the climate control temp to hot. I bet if you listen closely you will hear air bubbles moving through the heater core.

 

Should it be possible to fill the cooling system without an airlift?

How come other 350z owners are able to fill their cooling systems without an airlift?

Thanks

 

This is the one I have

 

What makes you think they don't have air in their systems? Maybe just not as much as you?

 

If you can survive overheating issues, the air will eventually work it's way out. But see the beginning of this sentence.

 

On the cooling fan, check your fuses. My 350z shows two fuses but I have no clue on how to remove one of them. I blew one fuse on a particularly hot day.

 

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Completely possible as long as you do it right and are careful. If it's only overheating just a little you can still drive a bit longer but once the needle starts raising more and more immediately pull off to the side of the road and shut that car off wait for it to cool down for a little while, and if you don't have too much further of a drive